[4] In 1958–1959, Tube Investments, advised by S. G. Warburg & Co, fought a fierce and ultimately successful battle to acquire British Aluminium in a bidding war with a consortium of City of London bankers led by Morgan Grenfell.

In the early 1970s, S. G. Warburg entered into a U.S. joint venture with Paris-based Paribas (Banque de Paris et des Pays-Bas, prior to the bank's nationalisation in 1982) named Mercury Securities.

Although the joint venture initially provided an international dimension for its three members, the relationships soured in the late 1970s and early 1980s.

[8] The joint venture was plagued by competition between Warburg and Paribas, as well as cultural conflicts between French, English, and American executives.

[8][9][10] A major participant in the "Big Bang" reforms of the 1980s under the leadership of its chief executive Sir David Scholey, it acquired stockjobber Ackroyd & Smithers, stockbroker Rowe & Pitman, and the government gilt broker Mullens & Co. in August 1984.

[12] Following another flawed and costly expansion into the United States, in 1994 a merger was announced with Morgan Stanley, but the talks collapsed.